JPH05291746A - Manufacture of board with metal core for printed wiring - Google Patents

Abstract

PURPOSE:To obtain a board for printed wiring which has excellent heat dissipation and heat resistance and in which electric or thermal designing is facilitated and a through hole is easily formed by using a metal plate coupled by a coupler as a core material, thermosetting resin composition is molded, and then the coupler is removed. CONSTITUTION:A metal core is formed in a shape in which electrically or thermally isolated parts 1, 2 are coupled through a coupler 3. After the core is inserted, thermosetting resin composition is molded in a plate state, and the coupler is removed to electrically or thermally isolate part of the core. These three parts may be formed of different materials or the same. Or, they may be punched from one metal plate by punching or etching, or may be formed of two or more metal plates. Thus, excellent heat dissipation, heat resistance are obtained, and further electric or thermal designing of a board is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board used for electronic equipment and the like which requires heat dissipation and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a printed wiring board used for electronic equipment is laminated with paper or glass cloth (prepreg) impregnated with phenol resin, epoxy resin or the like and a metal foil, and heated and pressed by a press. Obtained. Such a substrate made of paper or glass cloth and resin has a low thermal conductivity and cannot be directly mounted with a large power semiconductor element or the like that generates a large amount of heat, but must be mounted separately on a heat sink or the like. On the other hand, there is a metal core wiring board as a wiring board having heat dissipation property, which is obtained by applying a resin on the surface of a metal plate to form an insulating layer and bonding a metal foil. With such a metal core substrate, circuits can be formed on both front and back surfaces, but it is difficult to form through holes for electrically connecting these because the metal plate is an electrical conductor. On the other hand, a method in which a through hole formed in a metal plate is filled with an insulating resin and then laminated with a prepreg (for example, JP-A-59-105216).
JP-A-59-213431, JP-A-59-213431 and JP-A-59-213432 have been proposed. However, since the prepreg is used in these methods, the resin filled in the through hole does not include the base material, and the physical properties such as the coefficient of thermal expansion are different from those of the insulating layer portion, and the electrical properties of the through hole portion are different. Anxiety remains in reliability.

[0003]

To solve such problems, there is a method of molding a substrate with a metal core by using a molding material. However, a thermoplastic resin such as polyresin, which is mainly used for general molding substrates, is used. The molding temperature of ether ether ketone, polyether sulfone, polyether imide, etc. is 3
It is very high at around 00 ° C and has problems in dimensional stability and the like. Further, since the melt viscosity is high, the metal core is easily moved and deformed by the molding pressure during molding. In addition, resins with good heat resistance are expensive. On the other hand, the thermosetting resin can lower the molding temperature and has good dimensional stability. Moreover, the heat resistance is good, but the price is low. On the other hand, when the metal core is composed of one continuous metal plate, the heat generated at a certain part on the substrate may diffuse to the other part through the metal core, which may unnecessarily raise the temperature there. Further, when the metal core is used as a part of the electric circuit, it is limited to only one wiring. For example, if multiple circuits such as a high voltage circuit and a low voltage circuit, an analog circuit and a digital circuit, etc. are on the same substrate and the ground potentials are different, use the metal core as the ground for only one circuit. I can't. Further, in order to improve the heat dissipation of the semiconductor element, when the semiconductor element is directly mounted on the metal core, the elements are short-circuited because the metal core is an electric conductor. The present invention has been made in view of the above circumstances, and provides a printed wiring board having a metal core, which is excellent in heat dissipation and heat resistance and whose metal core is partially electrically or thermally separated.

[0004]

That is, according to the present invention, a metal plate composed of a plurality of flat portions connected by a connecting portion is placed as a core material in a molding die, and then a thermosetting resin composition is injected. The present invention relates to a method for producing a printed wiring board with a metal core, characterized in that a part of the metal core is electrically or thermally separated by removing the connecting portion after curing by curing. Hereinafter, the present invention will be described in detail.

FIG. 1 shows an example of a metal core used in the method of the present invention. The metal core has a shape in which a portion 1 that is electrically or thermally separated and another portion 2 are connected via a connecting portion 3. After this metal core is inserted and molded into a plate shape using a thermosetting resin composition, a portion of the metal core can be electrically or thermally separated by removing the connecting portion.

The three parts may be made of different materials or may be made of the same material. Further, it may be produced from one metal plate by press punching, etching or the like, or may be produced from two or more metal plates. For example, a method in which a nest is fitted and fixed by a convex portion serving as a connecting portion, a method in which only the connecting portion is made of a material which is soluble in an acid, and the like can be mentioned. If the metal core consists of two or more metal plates, they are connected to each other by caulking, welding, fitting, etc.
It is preferable that the number is one. This is to improve molding workability and moldability. That is, when the metal core is composed of a plurality of metal plates, the work of disposing the metal plates on the mold takes a lot of time and labor, and the positional accuracy of the metal core tends to be uncertain. Further, the metal plate which is not fixed is apt to move and deform during molding. On the other hand, even if a plurality of metal plates are fixed to each other and are apparently one, they can be easily placed in the mold and are unlikely to move or deform during molding.

The shape of the connecting portion may be any shape as long as it is easy to remove after molding and does not significantly reduce the strength of the removed substrate. Further, the number is not particularly limited as long as it does not cause deformation of the metal core during molding, but as the number increases, the removal step also increases, so it is preferable that the number is small. The material of such a metal plate is copper,
Any material such as metal such as aluminum or iron, alloy such as stainless steel, or plating such as zinc, tin, and nickel may be used, but those used for parts that require heat dissipation have thermal conductivity. Higher is preferable. Further, the one used as a part of the electric circuit preferably has high electric conductivity. The surface of these metal cores can be subjected to degreasing, roughening, treatment with a coupling agent, etc., and the adhesiveness with the resin can be improved.

When a through hole is formed in a portion of the substrate where the metal core is inserted, it is preferable that the metal core be provided with a through hole or a notch having a diameter larger than the diameter of the through hole. By drilling holes in the resin that has hardened in the through holes or in the notches, it is possible to form through holes that maintain insulation through the metal plate that is the core material and the hardened resin.

It is preferable that the metal core is provided with a resin filling through hole for allowing the resin to flow during molding. The reason for this is that if the metal plate is deformed due to the deviation of the molding pressure during molding, if the metal plate has through holes with an appropriate density, the resin will flow through this hole and the deviation of the molding pressure will occur. It is possible to prevent the deformation of the metal plate. Further, since the upper and lower resin layers are bonded to each other through the through holes, it is possible to improve the strength against peeling and cracks in the thermal shock test, the solder heat resistance test and the like. From the viewpoint of heat dissipation, it is preferable that a part of the metal core is exposed. The reason for this is that by mounting the semiconductor element or heat dissipation plate directly on the exposed metal core, the thermal resistance generated in the insulating resin layer of the substrate is eliminated, and excellent heat dissipation can be obtained. The formation of such a portion where the metal core is exposed can be performed at the time of molding the substrate, and a new process such as counterboring is unnecessary. The forming method is not particularly limited, and for example, the inner surface of the cavity of the mold and / or the metal core is provided with a convex and / or concave shape, and the inner surface of the cavity is closely adhered to the metal core at the time of molding without exposing the resin. And a method in which a separable plate piece is placed between the inner surface of the cavity and the metal core for molding, and then the plate piece is removed to obtain an exposed portion.

As the thermosetting resin for the insulating layer, any resin such as phenol resin, epoxy resin, polyimide resin, unsaturated polyester resin and triazine resin may be used, and several kinds thereof may be used in combination. In particular, heat resistance in a system in which a phenol resin is mixed as a curing agent with an epoxy resin,
It has excellent electrical characteristics. Further, additives such as a curing accelerator that accelerates the curing reaction, a flame retardant auxiliary agent that imparts flame retardancy, a colorant, and a release agent can be appropriately mixed in these resins. By blending various fillers in such a resin system, the thermal conductivity can be improved and the thermal expansion coefficient can be matched with the core material. For example, inorganic materials such as fused silica, crystalline silica, alumina, silicon nitride, silicone,
Powders of organic substances such as Teflon can be used, and they may be used alone or in combination of several kinds, but those having a high thermal conductivity are preferable for the purpose of the present invention. The particle size of the filler may be any size that does not cause the gate of the molding die to be clogged, and the shape thereof may be any shape. The blending amount of the filler is not particularly limited, but is preferably in the range of 20 to 80% by volume in view of the melt viscosity of the resin composition, the thermal conductivity of the cured product, the thermal expansion coefficient and the like. When the filler is blended, a surface treatment agent typified by a silane coupling agent may be added in order to enhance the adhesiveness with the resin.

As a molding method, a general molding material molding method such as casting, transfer molding, injection molding or compression molding can be used, and heating or pressurization may be performed as necessary. After the molding of the substrate, the connecting portion of the metal core is removed, but this method is not particularly limited. For example, a method of making a hole with a drill, a router, etc., and a method of removing the material by using a mold that exposes the connecting portion and then removing the material by etching or punching can be used. For the circuit formation method,
A known method such as an additive method using electroless plating can be used. In addition, a metal foil for circuit formation is placed between the inner surface of the mold cavity and the metal core during molding, and integrally molded to obtain a copper-clad substrate, on which a circuit is formed by a known method such as etching. can do.

[0012]

The metal plate connected by the connecting portion is used as the core material, the thermosetting resin composition is used for molding, and then the connecting portion is removed to provide excellent heat dissipation, heat resistance, and electrical or thermal resistance. It is possible to obtain a printed wiring board that has a simple design and is easy to form through holes. That is, since the substrate is formed by using a metal core having good thermal conductivity as a core material, excellent heat dissipation can be obtained. Further, since a thermosetting resin is used, excellent heat resistance and arbitrary shape can be obtained. Furthermore, since the metal core can be partially electrically or thermally separated, the electrical or thermal substrate can be easily designed.

[0013]

The present invention will be described below based on examples.
The invention is not limited to this example.

Example 1 ESCN-195 (Orthocresol novolac type epoxy resin manufactured by Sumitomo Chemical Co., Ltd., trade name): 100 parts by weight HP-800N (phenol novolac resin manufactured by Hitachi Chemical Co., Ltd., trade name): 50 parts by weight Alumina powder: 950 parts by weight Epoxy silane coupling agent: 3 parts by weight Triphenylphosphine: 5 parts by weight Carbon black colorant: 1 part by weight The above compounds were sufficiently kneaded to obtain a thermosetting resin composition.
On the other hand, on a copper plate with a thickness of 1 mm, which has a through hole for forming a through hole with a diameter of 1.5 mm, open three 12 mm square through holes in which four protrusions with a width of 1 mm and a length of 1 mm are exposed. A copper plate having a thickness of 1.6 mm and a size of 10 mm was fixed inside to obtain a metal core. The metal core and two pieces of metal foil having a thickness of 35 μm were placed in a mold having a cavity having a depth of 0.3 mm both at the top and bottom.
The above resin composition was transferred thereto by a transfer press at 175 ° C. for 9 minutes.
After being transferred for 0 second, the molded product was cured at 175 ° C. for 5 hours to obtain a copper-clad substrate with a metal core of 1.67 mm thick and 100 mm square. A metal core was separated by drilling through holes having a diameter of 1.5 mm at four portions corresponding to the protrusions of the metal core of the obtained substrate.

Example 2 The same method as in Example 1 was used except that as the metal core, one aluminum plate with a thickness of 1 mm was used, which was perforated in the same pattern as the projected view of the metal core used in Example 1. A copper clad substrate with a metal core was obtained.

Comparative Example 1 A dicyandiamide curing type epoxy resin varnish having a thickness of 0.
After impregnating a 2 mm glass cloth, it was dried to obtain a prepreg. Eight sheets of this were laminated, the copper foil used in Example 1 was placed on both sides, and heated at 170 ° C. for 90 minutes and pressed to obtain a copper-clad laminate having a thickness of 1.67 mm.

Comparative Example 2 A dicyandiamide curing type epoxy resin varnish having a thickness of 0.
After impregnating a 1 mm glass cloth, it was dried to obtain a prepreg. One piece of this prepreg and one piece of copper foil used in Example 1 are arranged on one side of an aluminum plate having a thickness of 1.5 mm, and molded in the same manner as in Comparative Example 1, and laminated with an aluminum base copper layer having a thickness of 1.64 mm. I got a board.

Comparative Example 3 Molded in the same manner as in Example 1 except that one copper plate having a thickness of 1 mm and having a through hole for forming a through hole having a diameter of 1.5 mm was used as a core material, with a metal core A copper-clad substrate was obtained.
However, no holes were made to separate the metal core.

Using the copper-clad substrate obtained as described above, thermal conductivity, solder heat resistance, and through hole formability were evaluated. The thermal conductivity is 100 mm without the copper foil.
The square substrate was measured with a thermal conductivity meter (QTMD3: manufactured by Kyoto Electronics Manufacturing Co., Ltd.) by the hot wire method using a plane probe.
Solder heat resistance is measured by cutting a copper-clad board into 25 mm square pieces, humidifying them in a high temperature and humidity bath at 85 ° C and 85% RH for 50 hours, and swelling after floating in a solder bath at 300 ° C for 5 minutes. Was visually observed. The evaluation of the through hole formability was performed by electroless copper plating the inner surface of the hole, using a drill to form a plated through hole, and observing the cross section with a microscope.
The results are shown in Table 1.

[0020]

[Table 1] * 1 Measured on the exposed part of the metal core (value is too high and out of measurement range)

As is clear from Table 1, Examples 1 and 2 and Comparative Examples 2 and 3 produced by the method of the present invention had higher thermal conductivity than Comparative Example 1 and good heat dissipation. In particular, in the exposed portion of the metal core of Example 1, there was no insulating resin layer and the thermal conductivity of the metal itself was high, which was a value that could not be measured by this measuring method. Further, in Examples 1 and 2, the respective core materials were thermally or electrically separated from each other. Furthermore, the formation of the through holes in Examples 1 and 2 and Comparative Example 3 is the same as Comparative Example 1
It was as easy as the above, and there were no voids or non-filling in the through holes, and the insulation was good.

[0022]

As is apparent from the above description, the metal core-containing substrate of the method of the present invention has a heat dissipation property equal to or higher than that of the conventional metal base substrate and is excellent in heat resistance, and is electrically or thermally Its industrial value is high because it is easy to design.

[Brief description of drawings]

FIG. 1 is an example of a metal core used in the method of the present invention.

[Explanation of symbols]

 1 ... Metal core A part, 2 ... Metal core B part, 3 ... Connection part

Claims (4)

[Claims] 1. A metal plate composed of a plurality of flat portions connected by a connecting portion is placed in a molding die as a core material, and then a thermosetting resin composition is injected and cured, and then the connecting portion. A method for producing a printed wiring board with a metal core, characterized in that a part of the metal core is electrically or thermally separated by removing. 2. The method for producing a printed wiring board with a metal core according to claim 1, wherein the metal plate is provided with through holes for forming through holes in advance. 3. The method of manufacturing a printed wiring board with a metal core according to claim 1, wherein the metal plate is provided with one or more through holes for resin filling in advance. 4. The production of a printed wiring board with a metal core according to claim 1, wherein a metal core and / or a molding die provided with a protrusion for forming a portion where the metal core is exposed is used. Method.